U.S. Pat. Nos. 4,751,319; 4,812,501 and 4,831,178 describe aliphatic and aryl esters of 1,3,2-oxazaphospholidines as color improvers and process stabilizers for various polymer substrates. The compounds described in these patents lack the benzo ring of the instant compounds, but are superior to the prior art compounds in stabilization effectiveness. The effect of the benzo ring is not obvious. There are electronic effects upon the heteroatoms (i.e. reduction in basicity of the nitrogen atom), changes in conformation and reactivity, the O--C.dbd.C--N fragment must be planar and a change in hydrolytic stability.
U.S. Pat. Nos. 3,574,797 and 3,773,711 describe 2-phenoxy-4,5-dibenzo-1-oxa-3-thia-2-phospholanes as polymer stabilizers. The instant compounds are structurally clearly different from the materials disclosed in these patents.
U.S. Pat. Nos. 3,632,690 and 3,796,684 describe substituted 4,5-benzo-1,3,2-dioxaphospholanes as polymer stabilizers. The instant compounds are structurally clearly distinguished from the compounds disclosed in these patents.
East German 146,464 and French 1,573,919 disclose 1H-1,3,2-benzodiazaphospholes as polymer stabilizers and antibacterials respectively. The instant compounds are clearly quite different from the compounds disclosed in these references.
There are a number of academic studies carried on in the Soviet Union on the preparation and physical properties of the 2-methyl, 2-ethyl, 2-isopropyl, butyl and phenyl esters of 4,5-benzo-1,3,2-oxazaphospholanes. These references are Zh. Obshch. Khim, 52, 1302 (1982); ibid, 43, 1860 (1973), ibid, 54, 1283 (1984); ibid, 53, 2468 (1983); ibid, 49, 955 (1979); ibid, 45, 266 (1975); ibid, 43, 2619 (1973); ibid, 42, 1901 (1972); and ibid, 55, 1184 (1985); and Chem. Abst. 73, 14858e (Soviet Union 245,101).
The instant compounds are structurally distinguished from each of the compounds disclosed in these prior art references and exhibit surprising stabilizing properties which further distinguish them from the prior art. This is manifested in the superior processing stabilization of polymeric substrates and in the maintenance of physical properties of polymeric substrates exposed to long-term thermooxidative stress.